Yun Wen

Zone division model for capacity analysis in multi-hop data acquisition systems with hidden nodes

Data acquisition systems play an important role in several industries. Because highly scalable ad-hoc networks with multi-hop transmissions can be easily constructed at low cost, such networks are considered suitable for data acquisition systems. However, a lack of centralized control makes it difficult to respond to congestion when system capacity is exceeded. Therefore, the estimation of system capacity is a critical issue for system design. In this paper, we propose a novel zone division model to analyze the capacity of multi-hop data acquisition systems using Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocols. We divide the one-hop area to a gateway (GW) into two zones: (1) an outer zone where an access node (AN) can relay packets from multi-hop ANs; and (2) an inner zone where ANs cannot relay packets. Using this approach, we calculate packet loss for each zone, considering the difference in the communication range of the GW and ANs, as well as the collision with hidden nodes. Simulation results show that our model achieves higher estimation accuracy than conventional methods, indicating that we have successfully modeled phenomena of the real system more accurately.

A Novel RAT Virtualization System with Network-Initiated RAT Selection between LTE and WLAN

Various radio access technology (RAT) selection methods between LTE and wireless LAN (WLAN) have been proposed, which aim to improve the capacity of the cellular network and to improve user satisfaction through mobile network operators. However, studies from the viewpoint of mobile virtual network operators (MVNOs) have not yet been investigated sufficiently. We propose a novel RAT virtualization system suitable for MVNO composed of a new network-initiated RAT selection method and RAT selection algorithms. The system conceals a change of IPs associated with a change of RATs and offers a context-aware virtualized RAT for the application server and user application. We demonstrate a new RAT selection method by developing a prototype of the proposed RAT selection system. We also evaluate a system-level performance by using a network simulator (NS-3) and show that our proposed algorithm outperforms conventional algorithms in terms of the WLAN usage ratio and user satisfaction.

Access Point Initiated Approach for Interfered Node Detection in 802.11 WLANs

Automated interference detection is required for operation and management services in wireless networks as Wireless Local Area Networks (WLANs) based on IEEE 802.11 Standard since co-channel interference from other wireless transmitters occurs irregularly. We propose a new approach for detecting the presence of interference on 802.11 links. Our solution focuses on the Access Point (AP)-initiated monitoring approach without Wireless Station (STA)-initiated additional function and sniffer devices. Our approach uses the geographical distribution of the response delay of the Acknowledgment packet (ACK) to the downlink packet that AP transmitted to STAs. The proposed method consists of a continuous monitoring step and a periodical diagnosis step to measure network statistics by ACK response delay between an AP and STAs and to detect whether and where interference occurs respectively. Comprehensive simulation results show that the proposed approach has a good accuracy and low misdetection ratio for diagnosing the interference existence and location in IEEE 802.11 WLANs.

A Transmit Power Control Algorithm for Data Acquisition Systems

Recently, wireless many-to-one networks have been attracting much attention and wireless sensor ad-hoc networks are applied to various applications. In ad-hoc networks using carrier sense multiple access with collision avoidance (CSMA/CA), the capacity is drastically decreased by the hidden node problem. In this paper, we assume a many-to-one network and propose a transmit power control (TPC) algorithm to avoid the hidden node problem. In our proposed TPC algorithm, a 1-hop area, a forced multi-hop area, and a multi-hop area are defined. All nodes in the 1-hop area adjust their transmit power as they can sense each others transmit data, and all nodes in the forced multi-hop area and multi-hop area control their transmit power as they connect to a gateway (GW) with multi-hop and reduce the interference to nodes in the 1-hop area. The network capacity using the proposed TPC algorithm is evaluated by computer simulation. By this computer simulation, it is shown that the network capacity of TPC is better by about 2.6 times than that of No-TPC.

Automatic failure diagnosis for Wireless LAN systems based on distribution of responses from STAs

With increase in the use of Wireless LANs in the enterprise area, network systems are often scattered across multiple locations in a wide area. Hence, there may be cases where a network administrator manages multiple locations. When users complain about connectivity issues, network administrators are expected to diagnose these problems without disrupting the normal operation of devices such as wireless stations (STAs) or access points (APs). In such cases, an on-site failure diagnosis is both time-consuming and expensive. Thus, an automated diagnostic technique to identify the cause of failure is important. We propose a method that can automatically identify the cause of the connectivity issues. The proposed method does not introduce any additional monitoring device, or require any functionality to be added in the AP or STA. In our proposed method, we send test packets to all STAs periodically and analyze the distribution of the responses and the RSSIs (received signal strength indicators) of the STAs. This helps to distinguish whether the connectivity issue is being caused by an AP failure, STA failure, or by a coverage-hole, which is a lack of network connectivity in certain areas of a building. The experimental results show that our proposed method is effective for the detection of AP failures, STA failures, and coverage-hole failures. From the detection results of a long experimental trial conducted in an actual office environment, it was observed that the false-detection probability of AP failure was very low. The STA failure was reported to be 0.36%, which was assumed to be because of hardware switch-offs or false detections because STA breakdowns were not reported during the trial. The ratio of the status “AP failure or STA failure” in the total failure detection was about 11%. Therefore, our proposed diagnosis system can suggest the cause of failure with a probability of 89%.

Collision-Free Packet Retransmission Protocol for Wireless CSMA Systems

Recently, wireless networks using ISM band have been attracting a lot of attention. In these systems using carrier sense multiple access with collision avoidance (CSMA/CA), the packet collision and recollision between hidden nodes occur frequently and drastically decrease the network (NW) capacity. In this paper, we propose a packet retransmission protocol to avoid the packet recollision in 1 hop many-to-one network, in which all nodes send their packets to an access point (AP). In our proposed retransmission protocol, hidden nodes whose first transmitted packet is lost control their retransmission timing autonomously to avoid recollision with each other by using time lag between the finish time of their first transmitted packet and the received time of a collision inform signal, which is sent by AP to inform nodes about packet collision. The NW capacity using the proposed retransmission protocol is evaluated by computer simulation. And it is shown that the maximum network capacity of our proposed method is about 1.7 times better than that of the conventional method.

Energy-efficiency of load-balancing routing for wireless convergecast networks: Centralized versus distributed implementation

In a wireless convergecast network, load-balancing routing contributes to improving energy-efficiency by eliminating the difference of relaying load among one-hop nodes. Load-balancing algorithms can be operated by centralized and distributed implementation. Centralized implementation needs to collect global neighborhood information, which leads to a large amount of signaling overhead. On the contrary, distributed implementation can overcome such issue. However, it only achieves sub-optimal load-balancing. Thus, it is obscure that which type of implementation is more energy-efficiency. In this paper, a novel distributed implementation for load-balancing routing is proposed. We make a series of analyses of comparing the energy-efficiency between centralized and distributed implementation. The results show that, the overhead for constructing load-balancing routing via distributed implementation is always less than that via centralized implementation. However, the heaviest one-hop node in distributed implementation suffers from more loads so that according to its energy consumption, distributed implementation can maintain energy-efficiency only in the condition that routing update cycle is shorter than a threshold.

Low-overhead and high-accuracy failure detection method for wireless multi-hop ad hoc networks

One serious challenge of wireless multi-hop ad hoc networks is frequent link and node failures due to lossy wireless channels and low-cost hardware. Failure detection plays an important role in network maintenance. In order to reduce communication overhead, local-based failure detection methods conduct diagnosis processes in a local area. However, the overhead of them is still very large because several redundant detection processes are triggered for one failure by several nodes. In this paper, we present a new failure detection approach named Root Node Reduction (RNR), which can reduce the number of detection processes by a backoff scheme. Furthermore, we propose two additional strategies to improve diagnosis accuracy, including multi fusion which guarantees complete evidence collection, and multi report which improves the reception ratio of diagnosis conclusion report. The comparison results show that the performance of communication overhead, diagnosis accuracy and data packet reception is improved by these schemes.